1. Field
Example embodiments relate to a composition and an organic insulating film prepared using the same, an OTFT using the above insulating film, an electronic device using the OTFT and methods of fabricating the same. Other example embodiments relate to a composition, which includes an organic polymer material having a carboxyl group and an organic silane material having an electron-donating group in order to assure the stability upon exposure to air, and to an organic insulating film prepared using the same, an OTFT using the above insulating film, an electronic device using the OTFT and methods of fabricating the same.
2. Description of the Related Art
A thin film transistor (TFT), which is primarily used in display devices, may be composed mainly of an amorphous silicon semiconductor, a silicon oxide insulating film, and metal electrodes. Increasing the diversity of material, an organic thin film transistor (OTFT) using an organic semiconductor has been developed, and has been studied with regard to its applicability.
Such OTFTs are advantageous because a printing process, which takes place under atmospheric pressure, may be used, rather than a plasma-enhanced chemical vapor deposition process, which is the conventional silicon process. In addition, performing a roll-to-roll process using a plastic substrate may be possible, thereby decreasing the cost of fabricating the transistor.
Generally, organic semiconductor material, which is being studied for use in the channel layer of an OTFT, may be largely classified into low-molecular-weight or oligomer material and polymer material. Examples of the low-molecular-weight or oligomer material may include merocyanine, phthalocyanine, perylene, pentacene, thiophene and/or oligothiophene. According to the conventional art, the use of a pentacene thin-film resulted in increased charge mobility of about 3.2 cm2/Vs˜about 5.0 cm2/Vs or more. Furthermore, devices using an oligothiophene derivative had relatively increased charge mobility (charge mobility=about 0.01 cm2/Vs˜about 0.1 cm2/Vs) and on/off ratio, but a thin film formation process mainly depends on a vacuum process.
As the polymer material, a thiophene-based polymer may be used for manufacturing OTFTs. The OTFTs thus obtained may have properties inferior to those of OTFTs that use low-molecular-weight material but may be advantageous in terms of processibility because a large area may be realized at a reduced price through a solution process, e.g., printing. In this regard, the related art has described the experimental fabrication of a polymer-based OTFT using a polythiophene material, called F8T2 (mobility=about 0.01 cm2/Vs˜about 0.02 cm2/Vs). Further, the related art discloses the fabrication of an OTFT using regioregular polythiophene (P3HT) (mobility=about 0.01 cm2/Vs˜about 0.04 cm2/Vs). As mentioned above, although the polymer material has TFT properties, e.g., charge mobility, inferior to those of pentacene, which is a low-molecular-weight material, the polymer material may be used because the need for an increased operating frequency may be eliminated and TFTS may be inexpensively fabricated.
Like the organic semiconductor material for the channel layer as above, in order to inexpensively manufacture a flexible OTFT, material for an insulating film, which may be subjected to a solution process, may be researched. Further, a material for an insulating film that improves the performance of OTFTs may also be researched. With the goal of decreasing the threshold voltage, examples may be dielectric materials having a high dielectric constant (high-k), for example, a ferroelectric insulating film, including BaxSr1-xTiO3 (BST: Barium Strontium Titanate), Ta2O5, Y2O3, or TiO2, and an inorganic insulating film, including PbZrxTi1-xO3 (PZT), Bi4Ti3O12, BaMgF4, SrBi2(Ta1-xNbx)2O9, Ba(Zr1-xTix)O3 (BZT), BaTiO3, SrTiO3, or Bi4Ti3O12, of which part of the materials are applied to OTFTs comprising an active layer formed with pentacene. However, the inorganic oxide material may have no advantages in terms of process compared to using conventional silicon.
When the OTFT is widely applied not only to LCDs but also to devices for driving flexible displays using organic EL, a charge mobility of about 10 cm2/V·sec or more may be required. However, the organic insulating film used therein may have k of about 3˜about 4 and requires an increased operating voltage (about 30 V˜about 50 V) and threshold voltage (about 15 V˜about 20 V).
Moreover, since a solution process enables the inexpensive fabrication of displays having a relatively large area, a polymer insulating film may be a gate insulating film material. As such, when the polymer insulating film is thickly formed due to increased leakage current, an increased operating voltage may result. Therefore, the polymer insulating film may be formed into a thin film having a reduced leakage current and an increased capacity, and should be highly resistant to chemicals, e.g., acids or bases, so as not to dissolve in a solvent used in the preparation of electrodes and/or OSC using a solution process or a printing process.
When LCDs or OLEDs are operated, the operating voltage may increase in proportion to the difference between the voltage required for Ion and the voltage required for Ioff. Accordingly, upon the actual use of displays, the device may consume a relatively great amount of power, and may deteriorate, thus becoming unstable. Where hysteresis occurs, a rapid switching speed may not be realized and a display afterimage may undesirably remain. Upon exposure to air, because such a hysteresis phenomenon occurs due to moisture present therein, the development of an organic insulating film that may mitigate such a phenomenon may be needed.